P806: TRACKING THE CLONAL EVOLUTION AND DRUG RESISTANCE PATHWAY OF NEWLY DIAGNOSED MULTIPLE MYELOMA THROUGH SINGLE-CELL RNA SEQUENCING
Authors: Jian Cui, Shuhui Deng, Xiaoyun LI, Wenqiang Yan, Xin Gao, Lugui Qiu, Gang An
Journal: HemaSphere (2023)

Topic: 13. Myeloma and other monoclonal gammopathies - Biology & Translational Research Background: Myeloma cells respond differently to therapeutic pressure, with sensitive clones being cleared and some more resistant clones being screened as major clones after treatment. This phenomenon of clonal resistance and clonal evolution, in which different clones compete with each other and change before and after treatment, is the underlying cause of the failure of minimal residual disease (MRD) clearance and myeloma recurrence. Previous studies have confirmed that clonal evolution in MM occurs at the cytogenetic level as early as after induction therapy and that different patterns of clonal evolution have a significant impact on the prognosis of MM patients. However, there is a gap in the study of MRD compared to myeloma cells at diagnosis in terms of cell composition and transcriptional heterogeneity Aims: To elucidate the cellular composition, transcriptional differences, and interrelation ship with the tumor microenvironment between MRD and myeloma cells at diagnosis, we performed single-cell RNA sequencing on primary and post-induction therapy myeloma bone marrow samples. Methods: In this study, we collected paired bone marrow samples from 19 cases before and after 2-4 courses of induction therapy with the VRD regimen; and from 10 normal controls (8 of which were from the Human cell atlas database). We generated single-cell transcriptome libraries by the Single Cell 3’ Library Kit V3 (10x Genomics, CA, USA), following the manufacturer’s instructions. Once prepared, indexed complementary DNA (cDNA) libraries were sequenced on a NovaSeq 6000 platform (Illumina) with paired-end mode according to the manufacturer’s instructions. Seurat and Harmony were then applied to perform dimensionality reduction, clustering and visualization. Cellular composition was then compared between paired samples at diagnosis, and clonal architecture and clonal evolution were then tracked using InferCNV. The interrelationship between myeloma cells and the tumor microenvironment were studied by CellPhoneDB. Results: Three types of clonal evolution patterns were identified by comparing plasma cell genetic abnormalities and transcriptional differences before and after induction treatment: (1) MRD-negative patients exhibited a clonally clearance of residual plasma cells after treatment, while MRD-positive patients exhibited clonal resistance and clonal selection; (2) Clonal resistance cells showed high proliferation activity and unfolded protein-responsive drug resistance pathways were activated. And unfolded protein-responsive drug resistance pathways and the NF-kB signaling pathway were activated in clonal selection cells; (3) Clonal selection cells showed more significant cellular communication with the microenvironment cells. Summary/Conclusion: The application of single cell RNA sequencing allows for the observation of clonal evolution and the onset of drug resistance early after induction therapy. Clonal selection cells exhibit activation of unfolded protein responses while gaining support from the tumor microenvironmental, and the ability to gain growth signal support from the microenvironment is an important reason for the more selective advantage of clonal selection cells over clonal clearance/resistance cells.Keywords: Drug resistance, Microenvironment, Multiple myeloma